Multi-effect evaporator

ABSTRACT

A thermal desalination system adapted to produce distilled water from feed water which may be sea water, based on a forward feed evaporator made up of a main water feed line, a vapor feed line, a distilled water main line and any number of effect groups. The effect groups include any number of effects which in turn include vapor inlets, water inflow lines, concentrate outflow lines that drain into a common concentrate drainage line, a vapor and water outlet in fluid communication with the distilled water main line, and heat transfer means that condense part of an inlet vapor to produce the distilled water.

FIELD OF THE INVENTION

This invention relates to distillation installations and methods, inparticular a method using multi-effect evaporators.

BACKGROUND OF THE INVENTION

Distillation of water is a process in which various soluble materialssuch as salt, contaminants etc. are eliminated from water containingthese materials, leaving clean, usually drinkable water. One knownmethod for achieving such distillation relies on water evaporation, muchlike salt and scale being accumulated on the bottom of an electrickettle after water has evaporated. In this process during evaporation ofthe water, soluble materials that are not volatile remain in a solidstate residue, usually in the form of salt and scale, and are disposedof. The vapor can then be condensed back into a state of liquid,resulting in contaminant free water.

U.S. Pat. No. 3,868,308 to the applicant discloses a multiple effectevaporator system, comprising a housing and a plurality of effectsconnected in a series to one another, each effect having a plurality ofbundles of tubes. The system is built such that high temperature steamis introduced into the tubes of the first effect, while non-distilledwater is sprayed against the outside of the tubes, causing the vapor inthe tube to condense while evaporating a part of the non-distilledwater. The remainder of steam from the tubes of the first effect, alongwith the evaporated water outside the tubes enters the tubes of theadjacent downstream effect, while the remainder of the non-distilledwater which has not evaporated, is accumulated at the bottom of theeffect housing in the form of a concentrate and is moved to be sprayedagainst the outside of the tubes of the adjacent upstream effect and soon and so forth.

Once water has completed its passage through all the effects of theevaporator system, the process yields distilled water on the downstreamend of the evaporator and a warm concentrate in the form of a highlyconcentrated water solution of soluble materials on the upstream end.

SUMMARY OF THE INVENTION

According to the present invention there is provided a multi-effectevaporator adapted for distillation of water, comprising a plurality ofeffects connected in a series manner and arranged into groups includinga most upstream group and subsequent downstream groups, each grouphaving a most upstream effect and a most downstream effect and having acommon parallel water feed inlet adapted to supply all effects in thegroup with feed water; the evaporator further including a main feedwater line in fluid communication with the most upstream group; an arrayof heaters disposed along the line and adapted for heating the feedwater before its entry into the effects of the most upstream group; eacheffect comprising heat transfer means adapted to receive an inlet vaporand produce from the feed water a first outlet vapor, leaving theremainder of the feed water as a concentrate, and to condense a part ofthe inlet vapor to produce distilled water, leaving the remainder of thefirst inlet vapor as a second outlet vapor; each effect comprising meansfor forwarding the first outlet vapor into an adjacent downstreameffect, where it will constitute the first inlet vapor, and means forforwarding the second outlet vapor into one of the heaters for heatingthe feed water thereby; each group further comprising a pump adapted toextract the concentrate from the effects of the group and pump it intothe common parallel water feed of an adjacent downstream group; andmeans for collecting the distilled water.

In one embodiment of the invention, the heat transfer means in eacheffect comprises a plurality of tubes with inter-tube spacestherebetween, the tubes being adapted for receiving the inlet vapor, andcontacting the feed water to cause a heat transfer therebetween,resulting in the vaporization of a part of the feed water in theinter-tube spaces, to produce the first outlet vapor, leaving theremainder of the feed water as a concentrate, and resulting in thecondensation of a part of the inlet vapor in the tubes, to produce thedistilled water, leaving the remainder of the inlet vapor as the secondoutlet vapor. The tubes are further adapted for channeling the condensedwater and the second outlet vapor from one side of the effect to theother.

The parallel water feed inlet in each group of the effects may comprisedispersion means adapted to introduce the feed into each of the effectsof the group so as to allow its contact with the tubes. The water feedmay be introduced into the dispersion means in various forms, e.g. thinfilm form, and temperatures, allowing optimization of the heat transferand overall desalination process.

The number of effects comprised in one group may vary according to thewater feed rate, water temperature and additional factors. The groupformation may hold up to 30 effects maintaining high efficiency factors.

The tube bundle may be of any material allowing reasonable heat transferbetween the vapor inside the tube and water on the exterior of the tube,such as aluminum or other metals or metal alloys. In operation, thetubes may be positioned horizontally or tilted at an angle as to aid thecondensed vapor within the tubes to flow down to the opposite end of theeffect by force of gravity. The tube shape is not restricted to acircular cross section and may be of other shapes, for example oval.

Further modifications may be made to the evaporator such asgalvanization of the condenser tubes, adding ion traps, using variousalloys for the condenser tubes etc.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, one embodiment of the present invention will now bedescribed, by way of non-limiting example only, with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic view of a multi-effect evaporator according to oneembodiment of the present invention, showing only the first and lasteffects of each of the groups;

FIG. 2 is an enlarged view of group 20 c with upstream and downstreameffects of the adjacent groups 20 b, 20 d of the evaporator shown inFIG. 1; and

FIG. 3 is a schematic view of a feed heater used in the multi-effectevaporator shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1 and 2 show a multi-effect evaporator system 10 together with itsmain water feed line 11 extending above and along the evaporator 10 fromits downstream end 10 b to its upstream end 10 a, and with its mainvapor feed line 12 associated with the upstream end 10 a of theevaporator. The evaporator 10 is adapted for the distillation of waterentering it from the main water feed line 11 using vapor entering itfrom the main vapor feed line 12.

The evaporator 10 comprises a housing 8 and four groups of effectsdesignated as 20 a to 20 d, disposed therein, group 20 a being theupstream-most group and group 20 d being the downstream-most group. Theevaporator 10 further comprises a condenser 13 adapted to condense vaporremains from the distillation process, a distilled water main line 16adapted to collect distilled water produced by the evaporator, a productpump 14 adapted to withdraw from the evaporator the distilled water, anda brine pump 15 adapted to withdraw from the evaporator brine left afterthe distillation. The condenser and both pumps are located at thedownstream end of the system.

The water feed line 11 is provided with a plurality of heaters 24, eachhaving a heater vapor inlet 41 adapted to receive vapor from each group20 and to heat thereby the water in the feed line 11. Each heater 24further comprises a first outlet 27 (shown in FIG. 3 and in FIG. 1 onlyfor the most upstream and downstream heaters of the groups 20 a and 20 drespectively) used for removing non-condensable gasses (NCG) andremaining vapor, in fluid communication with an NCG and vapor removalline 17, and a second outlet 44 for withdrawal of water therefrom.

Each group of effects 20 a to 20 d comprises a plurality of effects 30and a plurality of inlet chambers 40 connected in series with theeffects so that each effect 30 has on its upstream side an inlet chamber40. The effects are denoted E1 to E20, the most upstream and downstreameffects of each effects group 20 being designated as 30 h and 30 t,respectively. Groups 20 a, 20 b, 20 c and 20 d hold within them effectsE1 to E6, E7 to E11, E12 to E16, and E17 to E20 respectively.

Each of the effects groups 20 also comprises a common parallel waterinlet 25 divided into dispersion means 26, each adapted to introducefeed-water in a thin film form into one of the effects 30. Each group 20further comprises a concentrate drainage line 23 and a concentrate pump21 connected therewith, both adapted to withdraw concentrate from thegroup 20, the pump 21 being adapted to introduce the concentrate intothe water inlet 25 of the subsequent downstream group.

Each effect 30 comprises at its top a main water inlet 31 adapted toreceive water to be distilled from the dispersion means 26; a vaporinlet 32 located on the upstream side of the effect; and a concentratecollector 33 at the bottom of the effect in fluid communication with theconcentrate drainage line 23 of the effect's group. The vapor inlet 32of the most upstream effect 30 h of the first group 20 a is in fluidcommunication with the main vapor line 12, while the vapor inlet 32 ofeach of the other effects of each group is adapted to receive vapor, viaits preceding inlet chambers 40, from the immediately preceding adjacentupstream effect 30.

Within the effect 30 is located a tube bundle 35, consisting ofhorizontally coextending condenser tubes 35 a of oval or circularcross-sections, with a space 35 b therebetween. The upstream ends of thetubes 35 a constitute the vapor inlet 32 of the effect, and thedownstream ends of the tubes 35 a constitute a first, water and vaporoutlet 34 of the effect, for vapor and distilled water exiting thetubes, while the space 35 b between the tubes constitutes a second,vapor outlet 36 of the effect for vapor created from the feed water inthe space 35 b between the tubes 35 a. The tubes are slightly downwardlyinclined from the upstream side of the effect to its downstream side toallow water flow therein using gravitational forces. The tubes arelocated under the main inlet 31 to allow feed water from the dispersionmeans 26 to be sprayed thereon, to cause heat transfer between the vaporflowing within the tubes and the sprayed water. The ends of the tubes 35are supported by and arranged within vertical tube sheets 39.

Each effect further comprises a concentrate outflow line 37 whichconnects the concentrate collector 33 of each effect 30 with theconcentrate drainage line 23. The concentrate pump 21 of each group 20is connected to the downstream end of the drainage line 23.

As mentioned above, the inlet chamber 40 is disposed between each pairof two adjacent effects 30, one effect being on the upstream side of thechamber and the other being on the downstream side of the chamber. Thechamber 40 is adapted to receive water and vapor from first and secondoutlets 34 and 36 of the effect located on the upstream side of thechamber. The chamber is designed to allow vapor from outlet 34 to flowinto the vapor inlet 32 of the effect 30 located on the downstream sideof the chamber. The chamber also has at its top a vapor outlet 43 viawhich the vapor from outlet 36 is diverted to the vapor inlet 41 of thecorresponding heater 24. The chamber 40 further comprises a dropletseparator 38 located at the vapor outlets 34, 36 of each effect and adistilled water collector 42 located at the bottom of the chamber,adapted to receive the distilled water from the first outlet 34 of theeffect on the upstream side of the chamber. Connected to each distilledwater collector 42 is a distilled water outflow line 47 leading to thedistilled water main line 16.

It should be appreciated that although described here to be commonparallel drainages for both concentrate and distilled water, theconcentrate collectors 33 may be connected in series to one another, andthe distilled water collectors 42 may also be connected to one anotherin a series manner.

The heaters 24 may each be associated with one group 20 or with oneinlet chamber 40 of each group 20, as shown in the drawings.

The main water feed line 11 and vapor feed line 12 are connected to thefirst effect 30 h of the first group 20 a. The condenser 13 is in fluidcommunication with the water and vapor outlet 34 of the last effect 30 tof the last group 20 d via pipe-line 13 a and the brine pump 15 is influid communication with the concentrate drainage line 23 of the lastgroup 20 d via pipe-line 15 a.

In operation, feed water is introduced from an external source into thefeed line 11 on the downstream end of the system, at about 25° C., andpassed along the feed line 11 through the heaters 24. The heaters 24gradually heat the feed water until it is introduced into the commonparallel water inlet 25 and the dispersion means 26 of the first group20 a. The heating of the water is such that it reaches the first effect30 h of the first group 20 a at its highest temperature which may reach82-85° C. At the same time, vapor at a temperature slightly above 85° C.is introduced into the vapor inlet 32 of the first effect, i.e. into theupstream ends of the tubes 35 a of the first group 20 a.

The water from the feed line is sprayed downwards from the main waterinlet 25 using dispersion means 26 which spray it in thin film form,i.e. about 0.2-0.3 mm, onto the tubes 35 a of each of the effects 30 ofthe first group 20 a. Upon the contact of the water film with the tubes35 a, a heat transfer process takes place between this film and thevapor flowing within the tubes 35 a, resulting in partial condensationof the vapor in the tubes 35 and partial evaporation of the feed waterin the space 35 b between the tubes.

The vapor that has condensed in the tubes 35 a constitutes the distilledwater and flows by force of gravity down the tubes, which are inclined,into the inlet chamber 40 located at the downstream end of the tubes,where it drips down to the distilled water collector 42. The distilledwater flows down from the collector 42 of each inlet chamber 40 to thedistilled water main line 16 via the outflow line 47. The remainder ofthe vapor that has not condensed in the tubes 35 a, flows into the inletchamber 40 and is sucked via the vapor outlet 43 into the vapor inlet 41of the respective heater 24 that utilizes the hot vapor to heat the feedwater in the main water feed line 11.

The feed water that has turned into vapor in the space 35 b between thetubes 35 a of the effect is forwarded via the chamber 40 to the vaporinlet 32, and the upstream ends of the tubes 35 a, of the next,immediately adjacent effect. The feed water that has not evaporated,namely the concentrate, drips down to the concentrate collector 33 atthe bottom of the effect 30, from which the concentrate flows down intothe concentrate drainage line 23 of the first group 20 a.

The concentrate is then pumped from the concentrate drainage line 23using a concentrate pump 21 via pipe-line 22 into the common parallelwater inlet 25 of the second group 20 b, where the process is repeatedin this and subsequent groups, with the only difference between thefirst group 20 a and all the subsequent groups 20 b to 20 d, that thefirst group 20 a receives feed water from the main water feed line 11while the other groups receive feed water from the concentrate pumps 21.Thus, the feed water and the vapor both move downstream during theprocess, the evaporator system thus being a forward feed flowmulti-effect evaporator.

The feed heater 24 shown in FIG. 3 is adapted to receive feed waterthrough the inlet 11 a and hot vapor with NCG through the inlet 41 andallowing heat transfer between the two. This process yields heated feedwater leaving the heater 24 through the outlet 11 b and condensed vapor,constituting distilled water, leaving the heater 24 through outlet 44.The vapor that has not condensed is removed through outlet 27 via NCGand vapor line 17. The outlet 44 may be in fluid communication with thedistilled water collector 42 of the inlet chamber 40 or with thedistilled water main line 16.

The above described process produces distilled water and obtains themost highly concentrated brine at its lowest temperature due to theforward feed flow, as opposed to backward feed flow where the brine isproduced at the highest temperature. Low temperature brine allowspreventing the danger of scale and corrosion of the installation. Thebrine is removed from the system using a brine pump 15 via pipe-line 15a connected to the last concentrate drainage 23 d. At the downstream endof the system the distilled water from the distilled water main line 16is introduced into a condenser 13 via the pipe-line 13 a, where itutilized to condense the vapor coming from the last effect 30 t of thelast group 20 d. From the condenser 13, the product pumps 14 pumps outthe distilled water using the pipe-line 14 a.

The operation of the above described multi-effect evaporator 10 may befurther modified and enhanced by various means such as ion traps forheavy metals, pre-de-aeration of the water in a titanium tube, galvanicinsulation of tubes from tube plates by elastomeric grommets andincorporating sacrificial aluminum-magnesium anodes in the submergedsection of each effect. Furthermore, various types of water may be usedfor the process, the most common of which is sea-water. In addition,various numbers of effects for each group and, and a various number ofeffects altogether may be used in order to yield different results.

Those skilled in the art to which this invention pertains will readilyappreciate that numerous changes, variations and modifications can bemade without departing from the scope of the invention mutatis mutandis.

What is claimed is:
 1. A thermal desalination system adapted to producedistilled water from feed water, comprising a forward feed evaporatorcomprising a main water feed line, a main vapor feed line, a distilledwater main line and a plurality of effect groups, wherein each effectgroup comprises: a) a common concentrate drainage line, b) a parallelwater inlet, and c) a plurality of effects, each of said effectscomprising: i) at least one vapor inlet; ii) at least one water inflowline fed by said parallel water inlet; iii) at least one concentrateoutflow line draining into said common concentrate drainage line; iv) atleast one first vapor and distilled water outlet in fluid communicationwith said distilled water main line; and v) heat transfer apparatus forreceiving thereon feed water from said at least one water inflow line,and therein inlet vapor from said at least one vapor inlet and tocondense a part of said inlet vapor to produce distilled water to drainout of said at least one first vapor and distilled water outlet intosaid distilled water main line, leaving the remainder of the inlet vaporas a first outlet vapor, and to produce from said feed water a secondoutlet vapor, leaving the remainder of said feed water as a concentrateto drain out of said at least one concentrate outflow line; wherein saidmain water feed line provides feed water to the parallel water inlet ofa most upstream effect group of said plurality of effect groups; whereinthe common concentrate drainage line of any upstream effect group feedsthe parallel water inlet of its adjacent downstream effect group suchthat said effect groups are serially connected through their respectivecommon concentrate drainage lines; wherein the concentrate temperaturedecreases from said most upstream effect group to a most downstreameffect group of said plurality of groups, while the concentrate becomesincreasingly concentrated from said most upstream effect group to saidmost downstream effect group where the combination of said decreasingtemperature and said increasing concentration minimizes corrosion andscaling in the effects.
 2. The system according to claim 1 wherein eachof said effects further comprise at least one second vapor outlet forexit of said second outlet vapor from said effect.
 3. The systemaccording to claim 2 wherein each of said effect groups furthercomprises an inlet chamber disposed between two adjacent effects.
 4. Thesystem according to claim 3 wherein said inlet chamber receives saidfirst outlet vapor and distilled water from said at least one firstvapor and water outlet of its adjacent preceding effect.
 5. The systemaccording to claim 3 wherein said inlet chamber receives said secondoutlet vapor from said at least one second vapor outlet of its adjacentpreceding effect and forwards said second outlet vapor into an adjacentdownstream effect, where it will constitute inlet vapor.
 6. The systemaccording to claim 3 wherein the main water feed line comprises at leastone heater.
 7. The system according to claim 6 wherein said inletchamber establishes a fluid communication between said at least onefirst vapor and water outlet of its adjacent preceding effect and saidat least one heater such that said first outlet vapor passes into saidheater.
 8. The system according to claim 3 wherein the inlet chamberconsists of a droplet separator, and wherein the droplet separatorestablishes a fluid communication with said at least one first vapor andwater outlet and said at least one second vapor outlet.
 9. The systemaccording to claim 3 wherein the main water feed line comprises aplurality of heaters approximately equal to the number of effects in theevaporator.
 10. The system according to claim 9 wherein each of saidplurality of heaters comprises a main water feed line inlet, a mainwater feed line outlet, a heater vapor inlet, a distillate outlet and aheater vapor outlet, wherein said distillate outlet is in fluidcommunication with said distilled water main line, and wherein said feedwater is warmed by said first outlet vapor as it passes through saidheater and wherein a part of said first outlet vapor condenses toproduce heater distilled water which drains out of said distillateoutlet into said distilled water main line, leaving the remainder ofsaid first outlet vapor to form heater outlet vapor.
 11. The systemaccording to claim 10 wherein each of said inlet chambers in the seriesis configured to be in a fluid communication with a heater vapor inletof a corresponding heater.
 12. The system according to claim 1 whereinsaid common concentrate drainage line consists of a concentrate pump.13. The system according to claim 12 wherein the concentrate pump isconfigured to pump concentrate from the common concentrate drainage lineof an adjacent preceding effect into the water inflow line of anadjacent following effect.
 14. The system according to claim 1 whereinsaid main vapor feed line feeds inlet vapor into said at least one vaporinlet of said most upstream effect.
 15. The system according to claim 1wherein said most downstream effect is connected to a condenser andwherein said condenser is configured to condense the vapors coming fromsaid most downstream effect.
 16. The system according to claim 15wherein said distilled water main line is configured to be connected tosaid condenser.
 17. The system according to claim 15 wherein said heateroutlet vapor from the heater vapor outlets of the heaters are drainedinto a common vapor removal line.
 18. The system according to claim 17wherein the condenser condenses the heater outlet vapor of the commonvapor removal line.
 19. The system according to claim 1 wherein saidplurality of effect groups consists of 20 effects.
 20. The systemaccording to claim 1 wherein said feed water is sea water.